Abstract
Recent investigations have demonstrated that human milk contains a variety of bacterial genera; however, as of yet very little work has been done to characterize the full diversity of these milk bacterial communities and their relative stability over time. To more thoroughly investigate the human milk microbiome, we utilized microbial identification techniques based on pyrosequencing of the 16S ribosomal RNA gene. Specifically, we characterized the bacterial communities present in milk samples collected from 16 women at three time-points over four weeks. Results indicated that milk bacterial communities were generally complex; several genera represented greater than 5% of the relative community abundance, and the community was often, yet not always, stable over time within an individual. These results support the conclusion that human milk, which is recommended as the optimal nutrition source for almost all healthy infants, contains a collection of bacteria more diverse than previously reported. This finding begs the question as to what role this community plays in colonization of the infant gastrointestinal tract and maintaining mammary health.
Highlights
Due to the considerable health benefits it confers, human milk is universally considered the optimal source of nutrition for almost all healthy infants
Culture-dependant methods have long confirmed the presence of bacteria in aseptically collected milk including Staphylococcus and Streptococcus species [7], whereas culture-independent studies utilizing microbial characterization techniques based on the amplification of bacterial 16S rRNA have shown that human milk contains several additional genera of bacteria including Lactobacillus and Bifidobacterium [8,9,10]
With the exception of milk collected from one participant who donated only 2 samples, bacterial genomic DNA was extracted from milk samples collected at 3 time points over a 4-wk interval from 16 lactating women self-described as healthy and free from lactational mastitis
Summary
Due to the considerable health benefits it confers, human milk is universally considered the optimal source of nutrition for almost all healthy infants. Culture-dependant methods have long confirmed the presence of bacteria in aseptically collected milk including Staphylococcus and Streptococcus species [7], whereas culture-independent studies utilizing microbial characterization techniques based on the amplification of bacterial 16S rRNA have shown that human milk contains several additional genera of bacteria including Lactobacillus and Bifidobacterium [8,9,10] While these studies provide clear evidence that aseptically collected milk contains bacteria, very little work has examined the possibility that a core milk microbiome exists among lactating women, or investigated the stability of these communities within an individual over time. We hypothesized that human milk contains a greater diversity of bacterial phylotypes than previously noted, and that these communities would be stable over time within each individual lactating woman
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